In a driving machine, in which a driving device such as a servomotor is used, in a machine tool or a robot, for a diagnosis of a machine system concerning aged deterioration and a failure and a grasp of a characteristic change, it is conceivable to estimate and use a load characteristic such as friction of the driving machine.
One of related arts for performing a grasp of characteristic fluctuation of a machine system is explained (see Patent Literature 1). In the related art, a speed trapezoidal wave command is created in advance for an action of a driving machine, a motor is caused to operate based on the speed command, and motor speed and a torque command at the time of maximum motor speed (i.e., at the time of constant speed) for the command are stored. After the motor speed and the torque command are stored using a plurality of speed trapezoidal waves having different maximum speeds, the motor speed and the torque command are displayed on a monitor. A coefficient of viscosity and static friction of the driving machine are identified using a stored plurality of motor speeds ω and a stored plurality of torque commands Tr and used as indexes representing characteristics of the machine system.
The related art indicates a method of periodically storing, one week and one month after initial operation, data of the motor speeds ω and the torque commands Tr measured using the speed trapezoidal waves having the different maximum motor speeds and the coefficient of viscosity and the static friction estimated from the data, and comparing values of the coefficient of viscosity and the static friction and values designated by a manufacturer to grasp fluctuation in characteristics of the driving machine and determining whether the characteristics are normal or abnormal.
One of related arts for sequentially estimating friction of a driving machine is explained (see Patent Literature 2). In the related art, an estimating apparatus includes a disturbance observer unit configured to receive a torque command Tr and motor speed ω of the driving machine and output a disturbance estimated value Td^ that is an estimated value of disturbance torque Td (in this application, equivalent to load torque), which is torque applied to a motor from the outside, a disturbance-torque estimating unit configured to receive the disturbance estimated value Td^ and the motor speed ω and calculate a coefficient of viscosity D and a constant term C of a disturbance torque model Tdm obtained when the disturbance torque Td is approximated by a speed-dependent linear expression model as indicated by Formula (1), and an inertia identifying unit configured to receive an output of the disturbance-torque estimating unit, the torque command Tr, and the motor speed ω and identify inertia Jn.
                              T                      d            ⁢                                                  ⁢            m                          =                              D            ·            ω                    +                      C            ⁢                          {                                                                                          D                      =                                              D                        p                                                                                                                        C                      =                                                                        C                          p                                                ⁡                                                  (                                                      ω                            ≥                            0                                                    )                                                                                                                                                                                D                      =                                              D                        n                                                                                                                        C                      =                                                                        C                          n                                                ⁡                                                  (                                                      ω                            ≤                            0                                                    )                                                                                                                                                                            (        1        )            
The disturbance observer unit removes, based on the inertia identified value Jn identified by the inertia identifying unit and motor acceleration “a”, which is a time difference value of the motor speed ω, a torque component required for acceleration and deceleration of inertia from a torque command and outputs the disturbance estimated value Td^, which is an estimated value of disturbance applied to the driving machine, such as friction and a weight load. If there is an error between an actual value J of the inertia and the inertia estimated value Jn, the disturbance estimated value Td^ is represented by Formula (2) shown below and has inertia error disturbance in a second term. When the driving machine is not a simple rigid body, an error also occurs in Td^.Td^=Td+(J−Jn)·a  (2)
The disturbance-torque estimating unit applies an adaptive identification rule to the disturbance torque model Tdm obtained by approximating the disturbance torque Td with the speed-dependent linear expression as indicated by Formula (1) and sequentially calculates and estimates each of a coefficient of viscosity Dp and a constant term Cp obtained when the motor speed ω is positive and a coefficient of viscosity Dn and a constant term Cn obtained when the motor speed is negative. The constant term C is obtained by combining a torque component by a stationary gravity load and a torque component by Coulomb's friction that depends on an operating direction of the motor.
The estimating apparatus that estimates a viscosity term and a constant term according to the procedure explained above has already been proposed. Concerning the speed of the estimation in the related art, because the estimation of a characteristic of a change in a disturbance with respect to a change in the motor speed ω is performed, the estimation is normally performed at speed corresponding to a speed change of the motor, that is, a time constant equivalent to or shorter than a time constant of acceleration and deceleration. If there is an error in the inertia estimated value Jn, an error occurs in the disturbance estimated value Td^ as explained above. Therefore, an error also occurs in an estimation result of the disturbance torque command model Tdm represented by the viscosity term D and the constant term C. To cope with such a problem, in the related art, because an error of the disturbance estimated value Td^ is larger as the acceleration “a” is larger according to Formula (2), there is also proposed improvement for executing, only when the acceleration “a” is smaller than a predetermined threshold, the estimation of the viscosity term D and the constant term C of the disturbance torque model Tdm to reduce an estimation error.